1. Field of the Invention
The present invention relates generally to a method for managing a roaming subscriber in a VLR (Visitor Location Register) of a mobile switching center. More particularly, the present invention relates to a method for managing a foreign mobile subscriber in the VLR of a mobile switching center.
2. Description of the Related Art
In general, a mobile switching center (MSC) includes a first database for storing location information and the call details of a mobile terminal. The MSC is also connected to a second database in which information about a subscriber registered in its mobile communication service is stored. The first database in the MSC for storing the location information and the call details of the mobile terminal is called a VLR (Visitor Location Register), and the second database for storing subscriber information for the service of the MSC is called an HLR (Home Location Register). A network structure including such databases will be described with reference to FIG. 1.
FIG. 1 illustrates an MSC network structure including the VLR and the HLR. The structure and operation of the MSC network will be described below with reference to FIG. 1.
A mobile communication system includes MSCs, VLRs included in the respective MSCs, and an HLR having information about the subscribers registered in the MSC service provider. Each HSC is connected to a plurality of base station controllers (BSCs), and each BSC is connected to a plurality of base transceiver stations (BTSs). The BTSs are divided into their unique areas and perform radio communication with the mobile terminals of subscribers located in their areas. Therefore, a plurality of MSCs 100 and 200 are connected to one HLR 300, and each MSC includes its own VLR.
As shown in FIG. 1, the MSC 200 is connected to the BSCs 20-22, and the BSC 21 is connected to the BTSs 10-12. The BTS 10 performs communication with mobile terminals A11-A13 located in the area A. The BTS 11 performs communication with mobile terminals B11-B13 located in the area B. The BTS 12 performs communication with mobile terminals C11-C13 located in the area C. Furthermore, the respective MSCs 100 and 200 are connected a public switched telephone network (PSTN) 400 or an Internet network 500 for communication with them.
The mobile communication service provider establishes the BTSs, taking into consideration of the call quality and the number of the subscribers. Therefore, there is a case where a greater number of BTSs are established in a specific area while a smaller number of BTSs are established in another area. In this case, the area in which a smaller number of BTSs are established may have a non-serviceable zone. Hence, when a specific subscriber is located in the non-serviceable area, the subscriber is unable to make a call connection.
In order to circumvent the problem of subscribers being unable to make call when outside the serviceable area, different mobile communication service providers sometimes have an agreement between them to provide a roaming service so as to provide the subscriber's terminals of the other service providers with the communication service.
For example, referring to FIG. 1, if the subscriber B12 located in the area B is not registered in the HLR 300 but registered with another service provider, which has made an agreement on the roaming service with the service provider of subscriber B12, then the subscriber B12 can reasonably receive communication service via the service provider of the other company. This will be described below from the viewpoint of the VLR 250.
The mobile terminal uses a prescribed mobile subscriber identification number system, called “IMSI (International Mobile Subscriber Identification)”, for location registration. The IMSI number system is classified as shown in Table 1 below.
TABLE 1MINMCCMNCPLMNPFXRandom No.3 Digits2 Digits3 Digits3 Digits4 Digits
As shown in Table 1, the IMSI system is comprised of a mobile country code (MCC), a mobile network code (MNC), and a mobile station identification number (MIN). The MIN is comprised of a public land mobile network (PLMN) which is a service provider's number, a prefix PFX which is an office number, and a random number which is an individual identification number. That is, the mobile terminal performs location registration by transmitting the above 15-digit information to the BTS, and can receive the service from the service provider of another company.
However, not all the data provided from the mobile terminal is used when registering the data in the VLR. This will be described with reference to FIG. 2.
FIG. 2 is a table diagram for explaining a location registration and the search routine of a mobile terminal in the VLR according to the prior art. The location registration and the search routine of the mobile terminal will be described in detail below with reference to FIGS. 1 and 2.
Up until now, the national mobile communication service providers have not provided the roaming service to a foreign (i.e., internationally based) mobile communication service providers. Therefore, when a unique identification number of the mobile terminal is received at the VLR according to the IMSI system, it is determined whether the subscriber is a national subscriber, depending on the MCC and the MNC. When the subscriber is not a national subscriber, the corresponding data is discarded.
However, when the subscriber is a national subscriber, depending on the 3-digit PLMN, the VLR determines whether the subscriber is its own service subscriber or a roaming service subscriber. First, for the received PLMN data, a prefix index value is checked using a prefix table. That is, as shown in FIG. 2, an index “0” is assigned to a prefix “011,” an index “1” to a prefix “012” and an index “2” to a prefix “013.”
When the IMSI number received from the mobile terminal is “450 00 011 123 1234”, the MCCM+MNC number “450 00” is discarded and then the index number is searched using the number “011.” As shown in FIG. 2, the number “011” corresponds to the index number “0.” Accordingly, a method for searching subscriber data from the index table using the searched index number “0” for the number “011” can be calculated in accordance with Equation (1) below:LDN=(Index Value)×10000000+(PFX random No.)  (1). 
If this is substituted into Equation (1), then LDN=“0*10000000+1234567.” Therefore, a value “01234567” is obtained by performing the calculation. The corresponding data is searched from the INDEX-0 area of FIG. 2 using the subscriber's phone number. Alternatively, when the IMSI number received from the mobile terminal is “450 00 012 123 1234”, the index number becomes “1” in the above method, and a value “11234567” is obtained by performing the calculation of Equation (1). The VLR of the existing mobile communication system manages the mobile subscribers using this method.
It is possible to use such a method when providing the communication service to national (or domestic) subscribers only. However, when providing the roaming service to a subscriber of a foreign service provider as frequently requested these days, it is not possible to manage the data utilizing the present method. In order to solve this problem, the service provider needs to change the overall existing system, which, however, requires enormous expense.